Usually this pump stops when there is enough pressure in the circuit, so if your pump is constantly running the pressure in the circuit is too low and there are only two explanation: the pump is defective or there is a leak in the circuit.
The problem could be several different things. The first thing that comes to mind is the sensor. Have it checked out. A second problem might be that pressure is not building up in the water system. This could be due to leaking or a problem with the pump.
The most common cause for this to occur is that the pipe between the pump and pressure bottle have become porous and the water being pumped just leaks back to the well. The only solution is to replace the pipe. The replacement pipe should be plastic lined.
Potable water well pumps usually have a pressure switch after the output.
An output leak or a failed pressure switch will cause the pump to run.
Sump well pumps usually have a float switch in the well,
a failed or stuck float or switch will cause the pump to run.
This might happen if the switch is broken and the electricity is passed through the water pump regularly .You will have to check the wiring and the switch.
Your well pump is constantly running? How old the pump is? location? Only two things comes to mind. The underground water level is low, or the sensor is not working correctly. Get the installer to service the equipment
Bad check valve,foot valve,holding tank.First check the holding tank ,pump runs ,fills the holding tank, pump shuts off,tank should have 60 psi and hold pressure, if pressure starts to decrease with out faucets on see the the above. install a check valve before the holding tank